Fail-safe arc discharge lamp with integral arc extinguishing means



Aug. 9, 1966 J. G. RAY 3,265,917

, FAIL-SAFE ARC DISCHARGE LAMP WITH INTEGRAL ARC mxwmeuxsnme MEANS Filed Dec. 51. 1965 I NVEN TOR.

J15 6.3 I BY0 l y wpfln m United States Patent 3,265,917 FAIL-SAFE ARC DISCHARGE LAMP WITH INTE- GRAL ARC EXTlNGUISI-IING MEANS John G. Ray, Topsfield, Mass., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Dec. 31, 1963, Ser. No. 334,884 8 Claims. (Cl. 313-409) The invention relates to are discharge lamps, particularly fluorescent lamps.

Conventional fluorescent lamps, for example, comprise an elongate glass tube having terminal pins at each end for electrically and mechanically connecting the lamp in a fixture which has a ballast for limiting current through the lamp. From the terminal "pins lead wires extend through glass stem presses, which seal each end of the tube, to internal electrode structures each of which includes an emissively coated filament. In normal operation the filaments at each end of the tube readily emit electrons and support an arc discharge between filaments. However, the emissive material is consumed in operation and is ultimately exhausted. The filament then burns out and the arc strikes the internal electrode structure presenting several hazards. First the arc may hold on a particular part of the electrode structure, overheating and softening it so that it may fall against the glass wall of the tube cracking the wall. Part of the tube may then separate and fall from the end supported in the fixture by a terminal pin. If 'such a failure does not occur the arc may flicker causing eyestrain, or the ballast may overheat and fail. These hazards are particularly present in very high output (VHO) lamps drawing relatively high current.

The object of this invention is to prevent such a lamp from drawing current after its useful life has ended and to avoid the hazards described.

According to the invention an arc discharge lamp comprises a transparent arc tube, an insulating support wall sealing the arc tube, an electrode structure on said support wall including a portion inside the arc tube terminating in an emissively coated member and a portion outside said support wall, a part of said support wall being closely adjacent the outside portion of said electrode structure, and a conductor connected to the inside portion of the electrode structure and extending to said wall part, whereby when the emissive coating of said electrode member is consumed by operation of the lamp, the arc in said tube is directed by said conductor to and through said wall part to the outside portion of the electrode structure, thereby to extinguish the are by perforation of the wall.

For the purpose of illustration typical embodiments of the invention are shown in the accompanying drawing in which:

FIG. 1 is a view of a fluorescent lamp partly broken away to show in front elevation one form of an electrode structure according to the invention;

FIG. 2 is an enlarged vertical section through a part of the electrode structure of FIG. 1;

FIG. 3 is an enlarged side view of a part of the electrode structure of FIG. 1; .and

FIG. 4 is an enlarged elevation of a part of another form of electrode structure.

The fluorescent lamp shown in FIGS. 1 to 3 comprises an elongate glass tube 1 with a fluorescent coating on its inner surface, a fill of mercury and a small amount of inert gas such as argon, at low pressure. A glass stern press 2 makes a glass-to-gla-ss seal with each end of the tube 1. Nickel lead wire 3 and 4, about 0.030 inch in diameter, extend through each stem press from terminals 5 attached by an insulating nose 6 to a base 7. Each base is cemented to one end of the tube 1 and, as is Well known, nose 6 and terminals 5 are adapted to engage the ice socket of a lamp fixture so as tosupport the lamp mechanically in the fixture as well as to electrically connect the lamp to a ballast in the fixture.

The lead wires each have a portion, e.g. 3a, outside the stern press, that is, toward the end of the tube and exposed to outside atmosphere. From its outside portion 3a lead wire 3 extends through the stem press to an inside portion 3b connected to one end of an electron emissively coated filament member 8 and of an auxiliary electrode 9. The lead wire 3 also passes through a known shielding disk 11 to which it may be connected. Similarly the other lead wire 4 extends from a terminal 5, through the stem press 2 to the other end of the filament 8. An insulator 12 isolates the lead wire 4 from the disk 11.

The lead wires, shielding disk, filament and auxiliary electrode constitute a typical electrode structure shown for the purpose of illustration. Other electrode structures With more or fewer members may be used, and the present invention is applicable to fluorescent lamps which have only one terminal at each end, the second lead wire 4 having no electrical function or being connected to the one terminal pin.

In operation, the lamp as so far described has a small heating current applied through the filaments Sand a high voltage applied across the lamp in series with the two electrode structures. When the filaments 8 are heated to electron emission an arc is struck. So long as the filaments emit substantially more electrons than the other parts of the electrode structures, the arc will strike or hold only on the filaments. The emissive coating on the filaments is consumed during normal operation, and is eventually exhausted. The filaments are then burned up by the arc, and the other members of the electrode structure become significant electron emitters and are struck by the arc. The are may hold on one member, particularly one of' the lead wires, which then overheats and sags against the wall of the tube 1. As previously mentioned a large part of the tube 1 may then crack and separate from the supporting base, nose and terminals and fall from the fixture. Or a weak flickering discharge may continue until the ballast is damaged.

According to the invention as shown in FIGS. 1 to 3, an additional short conductor 13 connected at one end I to the inside portion 3b of lead wire 3 extends to a thin Walled part 2a of the stem press which lies closely adjacent the outside portion 3a of the lead wire 3 exposed to the atmosphere. It has been found that, although other parts of the electrode structure are closer to the arc, within a few minutes after failure of a filament the arc will strike the additional conductor 13 and will move down the conductor to its unconnected end. So directed by the conduct-or 13, the arc will then penetrate toward the exposed outside portion 3a of the lead wire 3, puncturing or perforating the thin walled stem press part 2a. Air will then enter the arc tube through the perforation and abruptly extinguish the arc.

Preferably the additional conductor 13 is a short length of nickel plated iron wire, 0.030 inch in diameter, welded to the inside portion 312 of lead wire 3. However, other conductors with substantially the same conductance as the lead wires may be used.

For example, as shown in FIG. 4 a conductive stripe is coated on the stem press, the stripe extending from the inside portion 3b of lead wire 3 to the above described part 2a of the stem press. The stripe may be applied as a colloidal graphite paint or as a mixture of metallic powder, such as nickel, and a suitable binder such as potassium silicate.

Any of the conductors described, by quickly extinguishing the are at the end of the lamps useful life prevent the lamp from cracking and falling from its fixture, eliminate weak or flickering operation and avoid damage to the ballast. The wire 13 of FIGS. 1 to 3 has the additional advantage that it may be attached to the electrode structure by well known mounting techniques, it is made of stock already used in electrode structures, and is extremely inexpensive.

' It should be understood that the present invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim:

1. An arc discharge lamp comprising a light transmissive arc tube, an insulating support wall having an insulative interior surface sealing the arc tube, an electrode structure on said support wall including a portion inside the arc tube terminating in an emissively coated member and a portion exposed to the atmosphere outside said support wall, a thin part of said support wall being closely adjacent the outside portion of said electrode structure, and a conductor electrically connected to the inside portion of the electrode structure and extending to and terminating in an electrically isolated end at said wall part, whereby when the emissive coating of said electrode member is consumed by operation of the lamp, the arc in said tube is directed by said conductor to and produces an opening through said wall part toward the outside portion of the electrode structure, thereby to extinguish the are by perforation of the wall.

2. An arc discharge lamp according to claim 1 wherein said conductor is a wire welded at one end to said inside portion.

3. An arc discharge lamp according to claim 2 wherein said conductor is nickel plated wire of substantially the same diameter as said inside portion.

4. An arc discharge lamp according to claim 1 wherein said conductor is a conductive stripe coated on said support wall.

5. An arc discharge lamp according to claim 4 wherein said stripe is formed of colloidal graphite.

6. An arc discharge lamp according to claim 4 wherein said stripe is metallic.

7. An arc discharge lamp according to claim 6 wherein said metallic stripe is nickel.

8. A fail-safe fluorescent lamp comprising an elongate glass are discharge tube; a glass walled stem press having an insulative interior surface extending into and bonded to each end of said tube to seal the interior of said tube; an electrode structure supported by each stem press, each said structure including at least one lead wire extending through the stem press with a portion outside the stern press and exposed to the atmosphere, a portion inside the stern press and an emissively coated filament on the inside portion of the lead wire, the wall of said stem press having a thin part closely adjacent the outside portion of said lead wire; at least one additional wire electrically connected to the inside portion of one lead wire and extending to and terminating in an electrically isolated end at said thin part of one stern press, said additional wire being of substantially the same electrical conductance as said one lead wire; and at least two terminal pins respectively connected to the lead wire at each end of said are tube and adapted to support the lamp in a fixture; said lamp normally operating with an arc discharge between said emissively coated filaments, and said are discharge striking .and heating the inside portions of said lead wires when the emissive coating on said filaments is consumed, said additional wire conducting said are to and produces an opening through the thin wall part of the stem press toward the closely adjacent outside portion of the lead wire, thereby to connect the interior of the are tube with the atmosphere and extinguish the arc discharge before overheated inside portions of the electrode cause the arc tube to separate from a supporting pin and drop from the supporting fixture.

References Cited by the Examiner UNITED STATES PATENTS 2,146,579 2/1939 Inman 313-109 2,422,828 6/1947 Eitel et al. 3l342 X 2,692,347 10/1954 Mason 313l09 JAMES W. LAWRENCE, Primary Examiner. GEORGE N. WESTBY, R. JUDD, Assistant Examiners. 

1. AN ARC DISCHARGE LAMP COMPRISING A LIGHT TRANSMISSIVE ARC TUBE, AN INSULATING SUPPORT WALL HAVING AN INSULATIVE INTERIOR SURFACE SEALING THE ARC TUBE, AN ELECTRODE STRUCTURE ON SAID SUPPORT WALL INCLUDING A PORTION INSIDE THE ARC TUBE TERMINATING IN AN EMISSIVELY COATED MEMBER AND A PORTION EXPOSED TO THE ATMOSPHERE OUTSIDE SAID SUPPORT WALL, A THIN PART OF SAID SUPPORT WALL BEING CLOSELY ADJACENT THE OUTSIDE PORTION OF SAID ELECTRODE STRUCTURE, AND A CONDUCTOR ELECTRICALLY CONNECTED TO THE INSIDE PORTION OF THE ELECTRODE STRUCTURE AND EXTENDING TO AND TERMINATING IN AN ELECTRICALLY ISOLATED END AT SAID WALL PART, WHEREBY WHEN THE EMISSIVE COATING OF SAID ELECTRODE MEMBER IS CONSUMED BY OPERATION OF THE LAMP, THE ARC IN SAID TUBE IS DIRECTED BY SAID CONDUCTOR TO AND PRODUCES AN OPENING THROUGH SAID WALL PART TOWARD THE OUTSIDE PORTION OF THE ELECTRODE STRUCTURE, THEREBY TO EXTINGUISH THE ARC BY PERFORATION OF THE WALL. 